I have an office with a ceiling of 4.5 m x 3.5 m and room height of 2.5
I would like advice on the no and rating of downlighters reqd to give a
good light to work by. Also I would like to dim them if reqd and
wondered if there was any particular dimmer charateristics to be aware
of And does a dimmer reduce the power consumption?
What sort of downlighters, halogens?
My advice would be to avoid them if you are expecting normal office
lighting levels. You need ridiculous numbers to get up to home
lighting levels, and office lighting levels are normally much higher.
Also, their colour temperature is rather low for an office.
You'll need an industrial sized dimmer if you are really going to
light a room that large to office lighting standards, and possibly
aircon to take the heat out of the room too.
Not by much, as they become very much less efficient when dimmed.
Dimming a 500W halogen down to similar light output to a 40W lamp,
and it will still be drawing something like 300W. A better way is
to have several separately switched circuits, and switch some off
to dim them.
Now there are downlighters designed for general lighting in offices,
and these (often called "cans", particularly in the US) usually take
a couple of compact fluorescent lamps. They are much bigger than the
halogen downlighters of the MR16 type often used at home. They are
available in dimming versions, but this is going to get expensive,
as you are now talking about a product only used in rather expensive
You will probably need to multiply this by another 4 or so to allow
for all the general lighting coming from reflections from the floor,
desktop, etc. This is where halogen downlighter efficiency is all lost;
the light source is at the best end of filament lamps, but the delivery
is completely wrong for general purpose lighting, and most of the light
is lost into the floor.
I would not recommend downlighters for general office lighting, particularly
if you will be using computers in the office. You will get a much better
working light from fluorescent lights fitted with anti-glare diffusers,
designed specifically for areas with computer use. If you are still using
CRT screens, high-frequency fluorescents are a very good idea, but I like
them anyway for the instant start and longer lamp life.
If you decide you really must have downlighters, you would do better to use
them for circulation lighting and to use local task lighting to bring the
workstations up to an acceptable light level. I suppose that, unless they
are low energy types, one advantage of using downlighters to achieve office
lighting levels is that you probably won't need to use any heating in the
What sort of downlighter do you want to use? The alternatives are broadly -
Halogen downlighters - small, but highly directional. Likely to create
strong pooling of the light and to make the ceiling look dark. Ratings
available from 10W to 50W. Using lots of low power ones will give a better
spread of light than a smaller number of high power ones. Flood types will
also give a wider spread of light than spot types. IMO the suitable only use
for halogen downlighters is display lighting, or where you need a very local
Mirror spot reflector lamps, usually around 50-65mm diameter. Ratings
available from 40W to 60W. These can be used in much the same way as halogen
lamps, but they give a light that is not so strongly directional.
PAR 38 spot or flood lamps. Rather old fashioned now, but the large diameter
does give a much better spread of light, particularly if you use the flood
version.. Ratings available from 60W to 120W. I have used four to light a 3m
x 4m kitchen.
Low energy downlighters. Usually the largest diameter fittings (the ones I
have are 135mm), but they are the only lamps that do not also produce
significant heat and they normally have the most diffuse spread of light.
Ratings available from 9W to 35W.
Tbe honest I was not aware there were all these alternatives but at
least now I will be able to have a meaningful conversation with the
local stockists THe low energy look favorite I will need to see how
they look what they cost etc
Not possible, halogen downlighters will never give you a decent light
to work by. By their nature theyre contrasty and glarey. Theyre used
for the look but are anything but ideal practical lighting. Dont
worry, theyre a fashion that will pass once people wake up.
Halogen downlighting is also one of the most energy inefficient
methods in current use.
Whatever light type you use, use a switchbank not dimmers. The result
with filaments: way more energy efficient, and more reliable
with fluoros: way cheaper and slightly more energy eficient
This is approx the same size as my kitchen, it's got 12 50W mains halogen
downlighters. It's very bright and I might change them to 30W once it's
finished. Anyone know where I can get hold of a 600W dimmer?
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